This invention generally relates to the field of cellular communication systems and, more particularly, to communicating position information of roaming mobile stations operating at remote service areas.
In today's cellular communication systems, the system operators have adopted communication protocols that allow them to offer various communication services while maintaining compatibility with services offered by other operators. One communication technology that is widely adopted is a Global Standard for Mobilecommunication, also known as the GSM standard or GSM. The GSM standard defines a radio communication protocol for a corresponding Public Land Mobile Network (PLMN) which is intended to provide local and roaming subscribers system access without compatibility problems.
The GSM is designed to support various communication services. For example, one of the communication services supported by the GSM protocol is a short messaging service (SMS) that allows system subscribers to communicate text messages with each other, over GSM signalling control channels. Because of increased sophistication in the services offered, some communication services now rely on position information that accurately characterize the coordinates of mobile stations within a service area. For example, position information is needed for fleet management of trucks and containers, preventing car thefts, locating rented cars and routing emergency calls. Generally, a PLMN that offers this type of service incorporates a Cellular Positioning System (CPS) that relates mobile stations' position information to a service requester when a position request is received. To provide the position information, the CPS includes a mobile positioning center (MPC) that initiates a positioning procedure to locate the mobile station in response to the position request.
It is customary for the MPC to transmit the position information to the service requester in absolute terms. Generally, however, the position information generated by the positioning procedure is in relative terms. To convert the relative coordinates into absolute coordinates, each MPC uses a distributed database consisting of a conversion table. Because the databases are distributed, each operator controls and administers its own database independent of other operators. As a result, the conversion from relative to absolute coordinates is performed by an MPC that covers the service area of a PLMN within which the mobile stations operate.
Conventional systems use a local MPC to initiate the positioning procedure for determining the relative coordinates of a mobile station travelling within a local service area. In a roaming situation, when the mobile station travels outside its local service area and into a remote service area covered by a remote PLMN, the local MPC may not be used for providing the position information of a roaming mobile station. Rather, the position request must be routed to the remote PLMN, which is usually operated by another operator. In response to the routed position request, a remote MPC can then initiate a positioning procedure for determining the position information of the roaming mobile station. Once determined, the position information must be routed back to the local MPC to be provided to the service requester.
Conventional techniques for handling communication with roaming mobile stations use a GSM Mobile Application Part (MAP) and/or other protocol that is based on a European standard known as CCIT No. 7. This protocol does not support the communication of position requests and location information between inter-networked PLMNs. Adding such communication capability to the existing GSM protocol is complicated and is likely to produce various compatibility issues with existing systems. Therefore, there is a need for a simple way of communicating position request and information between inter-networked LMPNs for roaming mobile stations in remote service areas, without compromising system compatibility.